Medical radionuclide imaging, commonly referred to as nuclear medicine, is a significant diagnostic tool that involves the use of ionizing radiation to obtain accurate, three-dimensional (3D) maps of an in vivo patient. Typically, one or more biologically appropriate radiopharmaceuticals are administered to a patient, as by ingestion, inhalation, or injection. Tracer amounts of these radioactive substances emanate gamma quanta while localizing at specific organs, bones, or tissues of interest (hereinafter collectively referred to as the “study area”) within the patient's body. One or more radiation detectors are then used to record the internal spatial distribution of the radiopharmaceutical as it propagates from the study area.
As the information is aggregated, it may be processed to create “static” 3D images of the study area. Temporal changes in the distribution's flux may be recorded to generate “dynamic” 3D images. When appropriately interpreted, these “maps” of the patient provide trained physicians insight into the patient's ultimate clinical diagnosis and/or treatment. Known applications of nuclear medicine include: analysis of kidney function, imaging blood-flow and heart function, scanning lungs for respiratory performance, identification of gallbladder blockage, bone evaluation, determining the presence and/or spread of cancer, identification of bowel bleeding, evaluating brain activity, locating the presence of infection, and measuring thyroid function and activity.
In order to screen out undesired, “background” radiation, conventional radionuclide imagers typically provide some means to restrict the ionizing paths of detected gamma quanta to those modes of propagation lying within a predefined range of acceptance angles. Such means typically comprise a set of barriers located in the direction of the ionizing source to substantially exclude gamma quanta not emanating along the direct paths from the study area to the radiation detector. Collimators, including an array of apertures, are customarily employed for this purpose.
Collimators are typically positioned so that undesired radiation is substantially absorbed before it can be detected. The direction (or incident angle) of unabsorbed gamma quanta is controlled by way of collimating aperture arrays that filter a radiation field before gamma quanta is detected. Collimators are typically manufactured from relatively dense (or high atomic number) materials so that undesired radiation is adequately stopped (or absorbed) before reaching the imaging detector. A variety of collimators exist, such as parallel-hole, converging (or diverging) hole, slant-hole, fan-beam, and pin-hole, as well as arrays thereof. These collimators come in a variety of materials, aperture diameters, aperture shapes, and thicknesses of aperture partitions, i.e., septa thicknesses.
One such radionuclide imaging technology that incorporates collimators is the gamma camera utilized in single photon emission computed tomography (SPECT) scanning. In SPECT scanning, a subject (or patient) is infused with a radioactive substance that emits gamma rays. Conventionally, a gamma camera includes a transducer to receive the gamma rays and record an image therefrom. In order for the image to be a true representation of the subject, a collimator having collimating apertures is positioned between the transducer and the subject to screen out all of the gamma rays expect those directed along a straight line through the collimating apertures between a particular part of the subject and a corresponding particular part of the transducer. Traditionally, the collimator is made of radiation opaque material, such as tungsten, tantalum, or lead, and collimating apertures have been formed therein.
For SPECT imaging to be realized, system designs generally require the gamma cameras to be supported on gantries that rotate the detectors through a specific angular range about the patient, usually covering one hundred eighty to three hundred sixty degrees of rotation. A drawback associated with this requirement, however, is that such gantries are relatively expensive subsystems of the diagnostic tool, because they must be capable of providing rapid rotation of large, heavy camera heads through very precise orbits about the patient.
Therefore, there exists a need for simplified medical radionuclide imaging apparatuses that can be economically and efficiently manufactured. There exists a particular need for such apparatuses that provide high image quality without camera head rotation.